let arr = [1, 2, 8, 3, 4, 5, 6, 7, 8]
function isIncrease (arr, len) {
  if (len === 1) {
    return true
  }
  return (arr[len - 1] >= arr[len - 2]) && isIncrease(arr, len - 1)
}
console.log(isIncrease(arr, arr.length));